Curable silicone compositions are used as sealing materials or protective coating materials for optical semiconductor elements in optical semiconductor devices such as light emitting diodes (LEDs). However, since the gas permeability of a cured product of a curable silicone composition is high, problems such as the discoloration of the sealing material due to corrosive gas and the reduction of brightness due to the corrosion of silver plate on the LED substrate occur when used in a high-brightness LED with high optical intensity and a large amount of heat generation.
Therefore, a curable silicone composition comprising a branched-chain organopolysiloxane having methylphenylvinylsiloxane units, an organohydrogenpolysiloxane, and an addition reaction catalyst is proposed in Japanese Unexamined Patent Application Publication No. 2012-052045 as a curable silicone composition which forms a cured product with low gas permeability.
However, such a curable silicone composition has high viscosity, poor handleability, and a slow curing reaction rate, which leads to the problem that a large amount of time and energy is required to complete the curing reaction.
An object of the present invention is to provide a curable silicone composition having excellent handleability and high reactivity and forming a cured product with low gas permeability. Another object of the present invention is to provide a cured product with low gas permeability and further to provide an optical semiconductor device with excellent reliability.